1. Field of the Invention
This invention relates to improvements in logarithmic amplifier circuits, and more particularly to improvements in quasi-open-loop logarithmic amplifiers that may be compensated for temperature changes and can perform true logarithmic amplification and exponential conversions.
2. Relevant Art
In the past, circuits used for logarithmic or exponential conversion of a signal were built from operational amplifiers in closed-loop structures, or derived from progressive compression techniques as cascades of open-loop gain stages. The closed-loop operational amplifier (the so-called "Patterson" or "transdiode" log amp) approach were typically slow, and the associated transfer function displayed an undesired temperature dependence and limited output voltage swing.
The progressive log amps alleviated these drawbacks at the cost of considerable circuit complexity and size, did not provide true logarithmic conversion, and, like the operational amplifier based circuits, were not easily adaptable to exponential conversion.